It's interesting. When Season 11 delved into Cath's connections with the casinos, I thought that would be a fitting and appropriate exit for the character. She's a strong broad, and would do well as a casino 'shark.' Casinos in Las Vegas make up a great percentage of the city's rich background and if Marg ever decided to return, the show wouldn't have to force a storyline to make the return work; the team could run into her at a crime scene or perhaps go gambling at one of the other casinos together. :lol:
CSI waned away from Grissom's roller coaster enthusiasm years ago, which was a real shame. I believe the last time it was really brought up was in Season 4's "Turn of the Screws." So, in my mind, I always felt that Catherine would decide to take more of a leadership position at one of Sam Braun's casinos, and after the team gets word of Catherine's resignation, they all go out for a celebratory evening and meet up with Grissom at one of the roller coasters located on the Strip. And as you see them all reaching the peak of the coaster--with the bright lights and electric atmosphere in the background--Grissom, sitting next to Cath, says something about this being "all yours." The roller coaster dips, the show fades to black, and that's the last of Catherine until something comes up. I understand Billy not wanting to overshadow these final episodes (and also needing to tend to his family), but a small scene would have been short, sweet, and not take the focus away.